Microporous marking structures for use with hand stamps are typically made of various polymeric materials and resin (i.e., thermoplastic resin) or other open cell compositions which combine to form a slab-like structure having a large quantity of microscopic pores. The microporous structure is typically impregnated with ink or other suitable marking fluid which fill many of the microscopic pores.
Hand stamps having microporous marking structures are commercially known as pre-inked hand stamps since they can be used to create numerous impressions without requiring a user to introduce additional ink into the marking structure. This function is due to the microscopic size of the pores which allow the ink initially retained therein to escape at a controlled rate.
One brand of high quality pre-inked hand stamps is manufactured and sold by M&R Marking Systems, Inc. of Piscataway, N.J. under the trademark ROYAL MARK. These pre-inked marking structures are made from ROYAL MARK brand gel which comprises a mixture of thermoplastic resin and ink. This mixture is also known as pre-mix used for manufacturing microporous marking structures.
Various methods of manufacturing such microporous marking structures exist. When microporous structures for use with currently available ROYAL MARK pre-inked hand stamps are manufactured, the pre-mix, which includes a desired quantity of ink, is poured into a mold. The mold is then heated in a vulcanizer at a predetermined pressure and temperature for a selected period of time. When this procedure is completed, the marking structure is formed into a microporous slab and it may then be removed from the mold. Typically, excess ink is then removed from the marking structure by a process known as stabilizing.
Another known method of manufacturing microporous marking structures contemplates initially forming a microporous structure which does not contain ink. Such microporous structures may be manufactured by sintering, salt-leaching or other methods. M&R Marking Systems also manufactures and sells this type of marking structures and associated hand stamps under the trademark OPTIMARK. This type of microporous structure is then impregnated with ink during a separate procedure which may require immersing of the microporous marking structure in an ink pool, subjecting the microporous marking structure and ink to a vacuum environment or other known methods. With this type of marking structure, it is also usually required to stabilize the structure (i.e., remove excess ink therefrom) prior to assembly on a hand stamp mount.
Regardless of whether the microporous marking structures have been manufactured from gel material where ink is initially impregnated therein, or whether they are initially formed without ink, such microporous marking structures have traditionally been secured to a hand stamp mount by using mechanical holding devices, such as a ring or a ledge which hold the edges of the marking structure in assembled position on the stamp mount, or by an adhesive material such as a cynoacrylate adhesive or other types of solvent based adhesive material.
Both of these types of securing procedures (i.e., mechanical or chemical) have been associated with certain problems. For example, drawbacks associated with the use of mechanical mounting mechanisms is that such mechanisms are costly in that they require additional parts and usually require more time to manufacture.
Several drawbacks have also been associated with the use of adhesives. For example, when marking structures which are initially formed with ink are desired, it is often to difficult to select a suitable adhesive which will create an adequate bond to the "wet" rear surface of the marking structure. This problem has been overcome by using selected types of adhesives such as cynoacrylates which adhere to certain wet surfaces. However, the use of cynoacrylates also have drawbacks in that they require skill when being applied to a marking structure in order to avoid a problem known as "blooming" where the cynoacrylate material works its way through the rear surface of the marking structure toward the front surface thereof. The cynoacrylate adhesive could then potentially seal off certain areas near the front surface of the marking structure thereby creating ink transfer problems. Also, the ink within the microporous marking structure may prematurely dry out as a result of the blooming problem.
With regard to marking structures initially formed without ink impregnated therein, such as those formed by a salt leaching process or sintering, double sided self adhesive pressure sensitive tape has been used to secure such marking structures to hand stamp mounts. Typically, it is required to apply such tape to the rear surface of the microporous marking structure prior to introduction of ink therein. Ink is then introduced into the marking structure, and the marking structure is then secured to a mount. The problem with this arrangement is that certain types of inks may cause the adhesive tape to be compromised and thus, the marking structure may loose its bond with the associated stamp mount.
Problems have also arisen due to certain adhesives which do not adhere well to wet surfaces. In order to overcome such problems, hand stamp manufacturers have sealed the rear surface of the marking structure with sealant material. When microporous marking structures are formed with ink introduced therein as part of the manufacturing process, hand stamp manufacturers have had to contend with the messy process of coating the rear surface of the marking structure with a sealant prior to the application of a suitable adhesive for securing the marking structure to a hand stamp mount.
When using other types of microporous marking structures which are not initially formed with ink therein, the sealing procedure may also be performed. However, it has been found that when ink is introduced into a marking structure after the rear surface has been entirely sealed with an appropriate sealant material, a problem known as "curling" has occurred. This problem arises due to the inherent swelling of the marking structure which occurs after ink has been introduced therein.